My best friend is a highly experienced civil engineer, specialized in designing intersections. His take on roundabouts:
- They are adored by urban planners because they look nice and you can put a statue or fountain in the middle
- They reduce T-bone collisions
However:
- Small fender benders and sideswipes are much more frequent
- They use way more area
- They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).
- Finally, they're also (mostly) worse for cyclists and pedestrians.
Essentially, they have use cases, especially in small towns, and they're pretty, but they're usually not the right engineering solution.
Not a civil engineer but as far as I know, the space is part of the point. If you keep the roads straight but just draw a circle in the middle, you don't have a roundabout. It only works properly if the drivers have to curve in and out of it.
You could keep the same space I guess by pinching the roads tighter near the entries/exits but I don't think anyone is talking about that.
The UK has mini roundabouts, which are just a painted white circle on the road: <a href="https://upload.wikimedia.org/wikipedia/commons/b/b0/Mini-roundabout.jpg" rel="nofollow">https://upload.wikimedia.org/wikipedia/commons/b/b0/Mini-rou...
Drivers treat them as a normal roundabout by giving way to traffic on the right.
I contest that drivers always treat it the same. They often go through the circle/cut th corner when there is low traffic, and I know at least one mini roundabout where traffic is way less frequent in one direction and the other direction is treated as the "main road" without slowing down.
propter_hoc · · focus · HN ↗
- They are adored by urban planners because they look nice and you can put a statue or fountain in the middle
- They reduce T-bone collisions
However:
- Small fender benders and sideswipes are much more frequent
- They use way more area
- They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).
- Finally, they're also (mostly) worse for cyclists and pedestrians.
Essentially, they have use cases, especially in small towns, and they're pretty, but they're usually not the right engineering solution.
MrSkelter · · focus · HN ↗
You can draw a circle on the road and have “roundabout rules” without the need for any car to even turn their wheels.
Lvl999Noob · · focus · HN ↗
You could keep the same space I guess by pinching the roads tighter near the entries/exits but I don't think anyone is talking about that.
scrlk · · focus · HN ↗
Drivers treat them as a normal roundabout by giving way to traffic on the right.
leni536 · · focus · HN ↗
I mostly like them though.